Why Wood Works: Rethinking Data Center Design

Our wooden foundation – Data Centers with up to 95% CLT

In the forests around our sites in Falun and Borlänge, the foundation for the future of critical digital infrastructure grows peacefully.

As a material, wood improves over time. The resin inside dries very slowly after the tree is felled, hardening the material from the inside the longer it stands. With reasonable maintenance, a wooden construction will outlast the generation who built it.

As Mattias Rantakallio, from construction partner ByggPartner says, wood means flexibility. “There is too much piping to do this in concrete", he starts.

If using concrete, "there is not enough time to decide on all the holes for pipes before the material and casting of wall elements are ordered.”

As one of the people responsible for building the two new data centers at the Falun campus, he has a clear view of the advantages of wood. 

He points out that the steps, decisions and actions connected to using concrete and steel prohibit a lot of the design choices EcoDataCenter wants to do, as well as specific customer demands that show up late in the fit out process. 

This is not new knowledge. ByggPartner and EcoDataCenter partnered up in 2017 to engineer a new direction for the data center industry by using more and more wood.

It was seen as unreasonable among industry representatives and data center customers to consider wood within mission-critical infrastructure.

World's first AI factory

Now, the wooden-based solutions in Falun works for the world’s most demanding customers, operations and loads, driving the AI revolution.

In May 2025, Europe’s first deployment of a liquid-cooled Nvidia GB200 cluster happened in Falun.

This led Nvidia CEO Jensen Huang to highlight EcoDataCenter as “the world’s first fully integrated AI factory” during his keynote speech at the Nvidia GTC in Paris in June 2025.

Cloud and AI leaders such as Microsoft and Meta have conceded that wood is the future for data centers, by building facilities that partially rely on wooden elements.

This quick shift is thanks to the innovation of EcoDataCenter together with partners, as well as the superior customer experiences from our sites. Our Net Promoter Score among customers for our project deliveries is 100/100, surpassing all other actors within the data center industry.

“Wood is extremely good when it comes to robustness. Much better than steel”

There is a strong sentiment, even within the construction industry, that wood is not safe.

The Swedish Council on Wood Construction highlighted in a Q&A session with Anders Rosenkilde, Adjunct Professor of Structural Engineering for Industrial Wood Construction at Lund University, the following:

“Wood as a load-bearing material in structures is just as safe from a fire perspective as other materials. There is a big difference between the combustible properties of the material and talking about how to achieve fire-safe structures. All materials have technical properties that must be taken into account when designing and building. Steel melts, concrete cracks, and wood chars. However, the properties of wood mean that it retains its load-bearing capacity for a long time if it burns, and its performance in terms of load-bearing capacity when exposed to fire is well known and can also be calculated.”

CLT was used in Germany, Austria and other parts of Central Europe during the 1990’s. But the mass market matured slowly, like forests, so production processes were not established enough to make it a cost-efficient alternative in the Nordics until the late 2000’s. Only then did large-scale production of CLT reach the wider construction market. 

“Now, it’s a very reliable material,” says Magnus Emilsson, CEO of Limträteknik and responsible for the technical construction of all EcoDataCenter buildings. 

“Wood is extremely good when it comes to robustness. Much better than steel”, explains Magnus.  

Robustness is one of three main fire safety criteria, the other two being origin and spreading.  

Some view wood as suboptimal in those regards. But when covered with non-flammable materials such as gypsum boards, the safety level of the bearing construction matches or exceeds that of widely used conventional materials. 

Magnus sums it up: “We build better wooden buildings than with conventional materials, because engineered wood (CLT) is a new method, so customers and regulatory bodies place higher demands on the material.” 

That, and because of unique wood properties (which we will see soon), EcoDataCenter’s buildings “could stand for hundreds of years, if maintained properly”, explains Magnus, and continues: “There is no built-in additional maintenance with a wooden building than with steel or concrete buildings”.  

The problem, he underscores, has not been that wood demands extra maintenance. It has rather been that conventional materials have been assumed to have little or no maintenance needs. 

It’s all about keeping the wood structures dry to ensure the load-bearing capacity is intact. EcoDataCenter has chosen an unconventional double layering of protection against water to guard the load-bearing capacity.

Driving safety development by choosing wood

But getting the materials and products needed for the wooden construction to meet fire safety standards was not easy. 

For example, the plastic PVC mats used in high-demanding environments like hospitals are tested and classified for concrete or steel structures. No supplier guarantees were initially given, if such a product would be put down on EcoDataCenter’s CLT floor tiles. 

“But we have insisted, in certain cases, to test materials for use in wooden constructions. The rationale for convincing suppliers has been our scale”, Magnus points out. 

“The sheer size of these projects have made possible an acceleration of the technological development," he adds.

"You have driven that in terms of wooden construction in general. There are more solutions available now than when you started.”

In late 2025, after more than a year of development, EcoDataCenter received four new types of doors developed from scratch in collaboration with local businesses – doors that fit wooden constructions perfectly and weigh less, to make working conditions for data center employees better.

But what about the unique wooden properties that heighten the fire safety level?

“The fire rescue services prefer wooden buildings" – How unique wooden properties heighten fire safety level

In a mapping of fire incidents in modern timber constructions by the Swedish state research institute Rise, the occurrence of fires in wooden constructions between the years 1996 and 2023 was significantly lower compared to the overall population of buildings.

In total, almost 95,000 fires were reported in Sweden between 1996 and 2023.

Out of these, 166 were recorded where wood was the load-bearing construction material. For this time period, only seven spreadings past the initial fire cell were observed.

There are many fire cells in data centers. But none extra due to the wooden construction.

This comes down to how CLT wood behaves when ignited, EcoDataCenter’s CTO Mikael Svanfeldt highlights. 

”During a fire, heat enters the wood. But what exits the wood are the gases freed through the pyrolytic process”, starts Mikael. 

The gases are the fuel for continued fire, he underscores. When wood is burnt, it chars.

“The charring has such a strong isolating property of the inner layers that the pyrolyse stops, so no new gases are emitted to continue the fire”. 

CLT wood is, essentially, self-defeating in terms of fire. The energy needed to uphold a sustained fire that can damage the construction core cannot be accessed due to the material’s charring properties. 

Mikael Svanfeldt mentions an incident from a wooden construction of a school building, where tool batteries charging overnight without fire alarms or supervision had ignited and started burning the wooden surface. But when workers arrived in the morning, all they saw was some charred, sooty wall planks. The remedy was simple: sandpaper.

Mikael relays something he picked up during construction discussions regarding one of the data centers in wood, where builders repeatedly said that CLT is a favorite for fire rescue services.

“It was as if they knew that the fire rescue services prefer wooden buildings over conventional materials,” he said.

"Wood is predictable" – The preferred material for the age of safe low-emission construction

Johannes Näslund, a fire engineer at the local fire rescue services in the Falun/Borlänge region, can understand the adage that firefighters prefer wooden constructions. “Wood is predictable”, he starts. 

Firefighters, fire engineers or fire safety consultants will have differing opinions on the relative usefulness, security and stability of wood compared to conventional materials, he injects. 

But in general, they all become more worried about heat and fire in constructions with steel than in similar wooden constructions. 

“We have a better opportunity to do our job safely and with proper risk evaluations when we come to wooden constructions”, Johannes says.

Steel loses its structural integrity around 500-550 degrees Celsius, but it is hard to determine its loadbearing capacity well before that in a fire scenario. And concrete dries out and cracks after sustained heat and fire exposure. 

Wood, on the other hand, and especially the CLT that is used by EcoDataCenter, behaves “nice and predictable” when ignited or heat-exposed. The surface chars, protecting the core of fresh, undamaged wood that keeps the elements structurally intact.

The standard fire curve, used to evaluate fire resistance in materials and buildings, is not fully applicable for wooden data centers, explains the fire engineer.

“Data centers are special,” says Johannes Näslund, “because of the size and purpose of the building. A likely fire scenario in this type of building can be expected to be less intense compared to the standard fire curve, which means that the robustness of the construction is better than what standardized tests measure.”

This means wooden elements perform better than expected in fire scenarios, setting CLT on par with conventional materials for safety.

In combination with fire suppression systems, good ventilation, high ceilings, and adequate fire cells, a fully developed fire in a wooden data center is “hard to imagine”, he says. 

He also adds that Swedish construction codes are material neutral. If a building meets the requirements for withstanding fire for one, two or four hours, you can use any material.

CLT fulfills all of the requirements and safety standards in the building codes across Europe, North America and Australia, making it the preferred material for the age of low-emission construction.  

Conclusion – Power Progress: The New Standard for AI Infrastructure

EcoDataCenter started in 2014 to rethink the data center industry.

Five years later, EcoDataCenter 1 opened: the world’s first large-scale data center built with cross-laminated timber (CLT), powered purely by renewable energy.

After a decade of engineering a new path for the industry, EcoDataCenter has proven that the scaling trilemma is possible to solve with wood.

Wood results in 30% faster builds with lower costs and improved operational efficiency.

The result is a data center design with a net effect of embodied carbon close to zero and 2650 tonnes of biogenic CO₂e stored.

Today, EcoDataCenter operates a 80MW site in Falun, with a 600MW mega campus taking shape in Borlänge.

By building with up to 95% wood, EcoDataCenter pioneers a new model for sustainable digital infrastructure, underpinning the world’s most advanced AI workloads for hyperscalers and AI pioneers.

That is how progress is powered. Purely.

Cost efficiency

• The cost-effectiveness and load-bearing strength of CLT make it 
  ideal for tall structures with wide spans.
• CLT's lighter weight lowers foundation and transportation expenses.
• Costs are expected to decrease as design familiarity and local 
  CLT supply grow.
• CLT allows for up to a 30% decrease in construction time, which 
  greatly cuts on-site labor costs.

Design

• Increasing the thickness of CLT panels allows for larger spans with lesser internal supports.
• CLT may be modified using basic tools when necessary.
• Similar to concrete slabs, 9-inch CLT panels may span up to 25 feet.
• Greater architectural flexibility in the arrangement of areas in the 
  design and layout of openings.

Shorter build times

• Faster occupancy and cheaper capital expenses are the outcomes of the shorter assembly time.
• Savings in time due to prefabricated design.
• Maximize off-site work, reducing noise, waste, and congestion for efficiency.
• Mechanical fastening technologies are employed in the assembly of CLT panels.
• CLT changes the design from "Frame" to "Plates".
• CLT floor construction might take up to four days, compared to 21 days for concrete.

Fire and safety

• The tightness between panels keeps smoke and fire from spreading and causing damage in certain locations.
• Because CLT panels burn slowly, their thick cross section offers 
  considerable fire protection.
• CLT provides superior fire resistance.
• Using a 7-inch-thick CLT wall specimen, the ASTM E119 fire resistance test took three hours, five minutes, and 57 seconds.

Thermal performance/energy efficiency

• CLT is very energy-efficient and capable of storing both heat 
  energy and moisture.
• The panel's thermal performance improves with increasing 
  thickness.
• CLT panels provide better insulation and lower U values, 
  lowering heating and cooling costs.
• CLT outperforms steel and concrete in terms of thermal characteristics.
• HVAC and lighting expenditures are reduced by 10% with a CLT 
  construction.
• CLT provides a tighter structure with fewer air leaks, enhancing 
  the thermal performance of the building.

Sustainability

• Decrease in the construction's overall environmental effect, 
  including recycling and disposal.
• In terms of embodied energy, water pollution, and air pollution, 
  CLT performs better than steel and concrete.
• CLT has a lower carbon impact since wood absorbs carbon from 
  growing trees.
• Wood production emits less greenhouse gases.
• Users associate greener buildings with healthier lives.
• CLT buildings use less energy to operate.
• CLT is an environmentally friendly, recyclable, and sustainable 
  building material with extended durability.

Minimal waste

• CLTs are designed for specific uses, resulting in minimal or no 
  worksite waste.
• Manufacturers can use manufacturing leftovers into staircases and 
  other architectural features.

Wind loads and seismic resistance

• A CLT-based structure resists lateral stresses.
• Seismic energy is dissipated via fastening systems.
• After being tested in an earthquake simulator, CLT constructions 
  revealed no lasting deformation.
• CLT operates exceedingly well in multi-story applications, with 
  negligible residual deformation.

Acoustic superiority

• CLT is considered a strong alternative to heavy-weight structures.
• Airborne and impact sound transmission is well controlled by 
  CLT structures.
• The higher the mass of a CCLT panel, the better its acoustic 
  performance.

Weight and mass

• CLT panels have a greater load-bearing capability relative to their own weight than the majority of conventional building materials.
• CLT weighs approximately four times less than concrete.
• CLT weighs up to 30% less than concrete and steel equivalents.

Structural integrity

• The most essential feature of CLT is its high strength-to-weight ratio.
• Buildings as tall as 150m might be designed using a combination of CLT and concrete.
• The stiffness of CLT panels is determined by the homogeneity of the individual layers.
• CLT panels perform effectively as load-bearing plates and shear panels due to their cross-laminated structure.

Adapted from D.R. Simeon et al (2024)